Article with corrosion-inhibited surface and composition for coating said surface



United States Patent ARTICLE WITH CORROSION-INHlBlTED sun- FACE AND COMPOSITION non coarnso SAID SURFACE I 7 Meyer J. Shnitzler, Brookline, Thomas it. Norton, West lfoxbury, and Richard McDonald, Scituate, Mass, as-

s gners to The Gillette Company, Boston, Mesa, a corporation of Delaware No Drawing. Application July 10, 1956, Serial No. 596,824

Claims. (Cl. 148-614) frictionally engaged by another metal part, they may perform a lubricating function.

A particularly important application of our invention resides in its use to prevent or inhibit the corrosion of steel razor blades, long a serious problem to blade manufacturers. I

Anti-corrosion oils conventionally employed to retard the corrosion of razor blades are reasonably effective as to temperate climates if the blades are individually wrapped and if unusual conditions are not encountered. In tropical countries, however, where conditions of high temperature and high relative humidity prevail, the protection afforded by these oils is inadequate, the resulting corrosion being most pronounced if the blades are stored, as is most usual, in the acidic atmosphere of a typical home medicine cabinet. When the blades are not individually wrapped, as is true, for instance, in the case of the dispenser type packages currently in vogue, the protection provided by anti-corrosion oils as presently compounded is insufiicient even for temperate climeshere again, especially Where the blades are exposed to the atmosphere of a home medicine cabinet.

A composition conforming to the present invention, which aims to overcome the deficiencies of the prior preparations, is characterized in that it incorporates, as components providing a corrosion-inhibiting effect, a plurality of carboxylic acids, at least one of which is employed in the form of a salt thereof with a bivalent metal, e. g., zinc, calcium, strontium, barium, magnesium, lead, iron, etc. Most suitably, the composition contains only two acids, one as such, the other in salt form. In any event, at least one of the acids must be an aromatic acid. When both are aromatic acids, they may be the same or diifercut. The acids must be stable both in the respect of their nuclear structure and in the respect of any substituents which may be present, i. e., they must remain integral under conditions encountered on use of the composition and must not enter into undesirable side reactions. In the preferred compositions, one of the acids is non-aromatic, while the other is selected from the class of aromatic acids consisting of unsubstituted monoand polybasic, mono-and polycyclic aromatic carboxylic acids and substituted monoand polybasic, monoand polycyclic, aromatic carboxylic acids in which one or more nuclear hydrogen atoms have been replaced with a hydroxy radical, an amino group, an alkyl group, an alkoxy group and/or a hydroxy alkyl group-provided, however, that ice 2 the total number of side chain carbon atoms, if any, should not exceed 12. Such substituted aromatic carboxylic acids may in some cases be preferred because of their reduced tendency to be dissolved or leached by Water or moisture. t

As exemplary of acids which may be used in the practice of the invention may be mentioned straight and branched chain acids of high, low and intermediate molecular weight, e. g., formic acid, acetic acid, n-valeric acid, i'so-valeric acid, capr'oic acid, capric acid, isoheptanoic acid, 2-ethyl h'exanoic acid, lauric acid, stearic acid, oleic acid, palmitic acid, ricinoleic acid, etc.; cyc1oparaitinic or alicyclic acids, particularly those having from 5 to 8 carbon atoms in the alicyclic ring, such as.

naphthenic acid, cfyclop'entane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid,

etc.; heterocyclic acids as alpha-furoic and isonicotinic acids; and aromatic acids such as benzoic acid, salicylic acid, phthalic acid, parotoluic acid, alpha-naphthoic acid, beta-naphth'oic acid, alpha-naphthalic acid, anthracene carboxylic acids such'as alphaand beta-anthroic acids, and the like.

Our researches indicate that the high corrosion-inhibiting value of our compositions derives from the formation therein of one or more complexescoinbining the acid components and from which acid molecules are gradually released in a discrete molecular form. Such a condition obviously would be optimal from the standpoint of prodnction on the metal surface desired to be protected of a film composed of a salt of the metal of the metal surface and one or more or the acid components-and it is our belief that the unusual results We attain are due to the development of such a film. In any event, we have found that nothing like equivalent. protection can be achieved through the use'of one of the acids alone or of (meet the metal salts alone. 1

That interaction between the acidcomponents, resulting in complex formation, occurs is indicated not alone by the unusually high corrosion-inhibiting value of the compositions as compafedwi'th compositions containing only one of the acid components but also by the fact that when the compositions aresubjected to heat, the aromatic acid component uses not tend tosublime or distill oil, whereas in the absence of the other acid component it is readily removed by distillation. Moreover, as employed together, the solubility characteristics of the acid components in organic solvents is substantially difierent from that of the component's 'separately'in the same solvents. That the complexes are not true chemical compounds is indicated by the fact that the unusual results can be attained using widely different relative proportions of the acid components. 1

Our compositions generally include an inert solvent acid as the aromatic acid constituent and mixed petro leum naphthenic acids as the non-aromatic acid constituent. It is unimportant which acid constituent is incorporated in the composition in the form of its salt with the bivalent metal, but we prefer to use the naphthenic acids in such form. An especially preferred composition for use on razor blades combines henzoic acid and zinc naphthenate.

The petroleum metal naphthenates are produced from naphthenic petroleum oils or petroleum oil fractions by processes which vary substantially in their details depending upon the metal desired in the product. Since these processes are Well known in the art it is unnecessary to describe them here. The crude zinc naphthenate prod not has much the appearance of molasses. Laid out as a film, either directly or from a volatile solvent, the film, although adhering Well to the surface over which it is spread, becomes quite hard on drying and the addition of benzoic acid in the usual quantities does not substantially alter this characteristic. Accordingly, when such a. film on the metal surface desired to be protected is considered objectionable, as is true in the case of razor blades, it is necessary to use a non-drying oil, grease, wax or other such. material as a base for the naphthenate-benzoic acid mixture. We prefer to employ for this purpose mineral oils having a Saybolt viscosity at 100 F. of the order of 65 to 75 seconds. In lieu of a mineral oil a fluid ester, for example synthetic ester oils such as the Z-ethylhexyl diester of adipic, azealic or sebacic acids, or silicone oils, or polyethers such as Ucon oils may be employed. Thus, we have found that di-(Z-ethylhexyl) sebacate may be used with excellent results. Razor blades treated with the compositions herein tend to retain their sharpness longer. since the edges better withstand the corrosive action of acids present in perspiration and sebaceous matter on the face.

Apart from razor blades our invention is considered especially valuable as applied in the manufacture of compounded oils for the internal lubrication of internal combustion engines. It is now quite generally recognized that the corrosion of the internal parts of such engines is due to the formation in the lubricating oil of combustion products of an acidic nature and the protective film provided by our compositions is highly resistant, as just indicated, to acid attack.

If desired, our invention may be applied as a means of increasing the effectiveness of compounded anti-corrosion oils heretofore available, although this'appears to be rather uneconomic in consideration of the fact that We have found little difference in effectiveness between compositions herein utilizing conventional anti-corrosion oils as the base or solvent for the active components and compositions herein based on straight mineral oils.

Each of the critical components of our most preferred composition, i. e., benzoic acid and zinc naphthenate, is of itself functional as a corrosion inhibitor. Used together, however, their combined effect is out of all proportion to the expected additive effect-a class phenomenon apparently due, as previously suggested, to the formation of one or more complexes combining both acid molecules.

It is our belief that the film produced on the metal surface by our most preferred composition is composed of a salt of the metal of the metal surface and benzoic acid. The thickness of this film being apparently about equivalent to that of a molecule of the metal benzoate, it appears from our results that the benzoate molecules must be extremely closely packed or interfitted-a condition which would manifestly demand deposition of the benzoic acid on the metal surface in discrete molecular form. Applying this theory to explain the relatively poor results obtained with solutions or dispersions of benzoic acid alone, one could reasonably say that in this case the benzoic acid molecules are deposited as aggregations incapable of such close interfitting.

Our invention, of course, is in no way predicated on the accuracy of the above or any other theory which may be advanced herein.

In preparing our preferred compositions, we ordinarily employ the acid and metal salt in equi-rnolecular proportions. The total concentration of the acid and metal salt in any solvent used may vary over a wide range depending on the identity of the solvent and on the degree of protection sought. If the composition is used at an elevated temperature, higher concentrations are, of course, possible. It is preferred to keep the concentration Within limits precluding the settling out of any material; indeed, an important advantage of our solventbased compositions as properly prepared resides in the fact that the active components do not tend to agglomerate and separate, a fault of many of the prior preparations.

Using the combination benzoic acid-zinc naphthenate, a greater quantity of the benzoic acid is immediately taken up by the solvent at room temperature, the temperature at which the compositions herein are normally employed, if the naphthenate and acid are previously mixed together with heatinga fact lending strong support to the complex theory. The effect obtains whether the mixing is carried out over a relatively short period i. e., 15-30 minutes) at a temperature of the order of 280 F. or over a relatively long period (i. e., 60-90 minutes) at a temperature of the order of 110 F. While one can quickly effect the taking up of a like quantity of henzoic acid by heating after the materials have been added to the solvent, the heat demand of such procedure is greater and it is accordingly less economical.

One or the other of the foregoing procedures is rec ommended whenever the composition is prepared for immediate use. Where this is not the case, one can simply allow the mixture of solvent, acid and naphthenate, whether the latter are added to the solvent separately or together, to stand at room temperature, most suitably with occasional shaking, until the apparent reaction between the naphthenate and acid is complete.

Where the solvent is non-drying, i. e., remains on the metal surface, adequate protection is in most instances conferred even though at the time of application of the composition the reaction between the active components is incomplete or has just started, since under normal conditions it will ultimately go to completion with production of the desired film. in the interval, protection may be provided, for the most part, by the non-drying carrier itself.

We have found in the case of our most preferred com position that solvents having a relatively low solvent power for benzoic acid generally provide better results than solvents having a relatively high solvent power for such constituent. The reason for this appears to be that in solvents of the former category, e. g., mineral oils, fluid esters, etc., the acid, for the most part, is maintained in the discrete molecular form in which it is apparently released from the assumed acid-salt complex. Using a solvent having a relatively high solvent power for benzoic acid (isopropyl alcohol or methyl ethyl ketone, for example), it is necessary for equivalent results to employ the active materials in substantially higher concentrations. Rest results are obtained with such solvents if, before addition of the combined materials, the solvent is first saturated with benzoic acid.

in most or" the compositions herein which include a solvent or carrier, the concentration of the aromatic acid constituent lies within the range 0.00l%-20%, and in every case, as will be noted from the following examples, the aromatic constituent, whether it be in the form of the free acid or the bivalent metal salt, is present in an amount least equal to the amount capable of saturating the carrier alone, i. e., in the absence of the other carboxylic acid or salt.

Apart from a solvent component, compositions within the scope of our invention may contain, in addition to the acid constituents, one or more auxiliary agents, such as antioxidants, stabilizers, antifreeze ingredients, etc., Whose function may or may not relate directly to the corrosion inhibition. Thus, one of our most effective compositions comprises, in addition to benzoic acid, zinc naphthenate and mineral oil, a petroleum sulfonate mixture which performs a stabilizing function. The analysis on this comarmor '2' position, which is particularly recommended for use on steel razor blades, is as follows:

Percent Zinc naphthena-te (14.5% Zn) 15.3 Benzoic acid 3.1

Sodium petroleum sulfonates (mol. wgt. 450-500) 4.6 Mineral oil 60.0 Mineral spirits 17.0

- Percent Zinc naphthenate (14.5% Zn) 16.0 Benzoic acid 3.2 Mineral oil 63.0 Mineral spirits 17.8

We have found that the acid corrosion conditions to which articles such as razor blades are often exposed in shipment, storage or use are well simulated in intensified form in the laboratory by the exposure of the blades to a humid atmosphere above a reservoir of an aqueous solution of acetic acid. The test which we customarily use and which is referred to in the examples below, submitted in further illustration of our invention, is described as follows: The equipment includes a l6-ounce jar within which are placed a l-milliliter beaker containing about 6 milliliters of acetic acid and two l-ounce jars, one of which contains 15 milliliters of water. The waterfilled jar rests with the beaker on the bottom of the 16- ounce jar, while the other small jar, which is to receive the test blade, is so supported from the bottom of the confining jar that its mouth lies just below that of the confining jar. The blade is prepared for testingby dipping or spraying the sharpened edges with the solution. It is then hung on a rod to drain and dry for from 30 minutes to an hour before it is introduced into the empty l-ounce jar. The covered assembly is kept in an oven at a temperature of 120 F. It is removed from the oven daily so that the blade can be examined for evidence of corrosion along its cutting edges.

Example 1 Benzoic acid was added to crude zinc naphthenate (a dispersion of zinc naphthenate in mineral spirits) with stirring and heating and the resulting mixture, containing 5 /2% benzoic acid, subjected to the standard test. No rust was noted until the fourth day. When the amount of benzoic acid was increased to 12.5%, there was no visible rust at the end of a month. The protection provided by zinc naphthenate alone was about one-half day, and benzoic acid alone similarly did not afford any appreciable protection (see Example 3).

Example 2 To a 6.5% solution of benzoic acid in di(2-ethyl-hexyl) sebacate was added a previously heated mixture of zinc naphthenate and benzoic acid containing 12.5% benzoic acid. The quantity of the mixture added was sufficient to increase the concentration of benzoic acid in the sebacate to 9.5%. The composition, when tested by the standard procedure, protected the blades against rusting for 18 days.

Example 3 A sample of mineral oil containing 3% benzoic acid without any metal naphthenate gave protection for a little over 2 days. A sample containing about 16% zinc naphthenate in addition to 3% benzoic acid gave 18 days protection.

Example 4 Conventional anti-corrosion oils, when tested according to the standard procedure,- conferredprotection for a fraction of a day. The addition of 3% benzoic acid in creased the protection to onefull day. No increase resulted from the addition of zinc naphthenate alone in any quantity. When 16% zinc naphthenate together with 3% benzoic acid were added "to samples of the same oils no corrosion was visible until about the fourteenth or fifteenth day.

Example 5 Commercial naphthenic acid and zinc b'enzoate were added to mineral oil with heating and stirring in equimolecular proportions. The resulting composition containing 3% combined benzoic acid, when tested by the standard procedure, gave just short of 20 days protection.

Example 6 A mixture of paratoluic acid, 3.5%, and zinc naphthenate, 24%, in di-(Z-ethylhexyl) sebacate still gave protection after 15 days.

Example 7 A mineral oil slurry of benzoic acid and zinc capryla'te containing 11% of the caprylate and 4.5% of the benzoic acid gave protection through 16 days.

Example 8 A mineral oil solution of calcium naphthenate and alpha-naphthoic acid, used in place of benzoic acid, was still effective after 5 days. The solution contained 20% naphthenate and 4% alpha napht hoic acid.

Example 9 A composition consisting of 1 part by weight of benzoic acid, 2.5 parts of Zinc benzoate and 20 parts mineral oil still conferred protection after 8 days.

Example 10 A straight mixture of benzoic acid and crude strontium naphthenate protected through 6 days. The mixture contained 12.5% benzoic acid. Using barium naphthenate in place of strontium naphthenate, protection was conferred through 28 days.

through and beyond 44 days and through 13 days, 'respectively. In each case the naphthen'ate was employed in the form of a dispersion of the .naphthenate in mineral oil, the form in which it is generally supplied commercially.

Example 11 A mixture of zinc benzoate and zinc naphthenate milk eral oil dispersion), 36% and 64%, respectively, conferred protection through 33 days.

Example 12 A mixture of lead benzoate, 36%, and calcium naph- I thenate (mineral oil dispersion), 64%, still conferred protection after 8 days.

Example 13 A strip of nickel metal coated with a formulation Example 14 An oil based composition containing about 16% zinc naphthenate and about 3% benzoic acid, after storage for upwards of 6 months, was free of any precipitate. On the other hand, samples of three conventional anticorrosion oils, after storage for the same period, were cloudy. A number of blades were coated with the stored oils and subjected to the standard test. The conventional Calcium and lead naphthenates with the same amount of benzoic acid gave protection I 5 7 oils all failed within 3 days, whereas blades coated with the zinc naphthenate-benzoic acid composition were still free of rust after 7 days.

Example 15 Steel razor blades coated with conventional anti corrosion oils showed corrosion after 2 days immersion in tap water at room temperature, whereas blades coated with a straight mineral oil solution containing 3% benzoic acid and 16% zinc naphthenatc showed no sign of corrosion after 22 days.

Example 16 The experiment of Example 15 was repeated using a 3% aqueous solution of sodium chloride rather than tap water. The blades coated with conventional anti-corrosion oils showed heavy corrosion after 2 days, whereas the blades coated with the straight mineral oil solution containing 3% benzoic acid and 16% zinc naphthenate showed no sign of corrosion after 7 days.

Example 17 Example 18 A mixture containing 3.84% zinc stearate, 0.74% benzoic acid, and 95.42% mineral oil gave more than 16 days protection, while the mineral oil containing the same quantity of either the stearate or the benzoic acid alone failed in less than 2 days. (The test procedure was the same as that in Example 17.)

Example 19 The following mixture still provided protection after 7 days (tested as in Example 17):

Percent Zinc naphthenate ..6.48 Benzoic acid 0.72 Mineral oil ..93.80

In each of the foregoing specific examples the aromatic acid or bivalent salt thereof is present in an amount at lest equal to that required to saturate the carrier alone; in several examples much more than this minimum amount is present. excess of the aromatic constituent may be used without any detrimental effect, there is no advantage in using more than is required to achieve the desired result.

Although specific embodiments of the invention have been described herein, it is not intended to limit the in vention solely thereto, but to include all of the obvious variations and modifications within the spirit and scope of the appended claims.

We claim:

1. A composition for application to a metal surface to retard the corrosion thereof which comprises an inert carrier and compounds providing a corrosion-inhibiting efiect a member of the class consisting of carboxyiic acids and bivalent metal salts thereof and a member of the class consisting of aromatic carboxylic acids and bivalent metal salts thereof, at least one of said members being present as a bivalent metal salt, the aromatic member being present in an amount at least equal to the amount capable of saturating the carrier alone.

2. A composition according to claim 1 in which the carrier is a mineral oil.

it will be apparent that while an I 3. A composition according to claim 1 in which the carrier is a fluid ester.

4. A composition for application to a metal surface to retard the corrosion thereof which comprises an inert carrier and, as compounds providing a corrosion-inhibiting effect, an organic acid and a bivalent metal salt of an organic acid, one of said acids being selected from the group consisting of alicyclic carboxylic acids having not less than 5 nor more than 8 carbon atoms in the alicyclic ring, the other of said acids being from the group consisting of unsubstituted aromatic carboxylic acids and aromatic carboxylic acids in which one or more nuclear hydrogen atoms have been replaced with a member of the class consisting of a hydroxy radical, an amino group, an alkyl group, an alkoxy group and a hydr0xyaikyl group-provided, however, that the total number of side chain carbon atoms, if any, does not exceed 12, the aromatic compound being present in an amount at least equal to the amount capable of saturating the carrier alone.

5. A composition according to claim 4 in which the carrier is a mineral oil.

6. A composition according to claim 4 in which the carrier is a fluid ester.

7. A composition for application to a metal surface to inhibit the corrosion thereof which comprises a mineral oil and benzoic acid and a naphthenate of a bivalent metal, the benzoic acid being present in an amount at least equal to the amount capable of saturatingthe mineral oil alone.

8. A composition according to claim 7 in which the metal of the naphthenate is zinc.

9. A composition according to claim 7 in which the metal of the naphthenate is calcium.

10. A composition according to claim 7 in which the metal of the naphthenate is barium.

11. A composition according to claim 7 in which the metal of the naphthenate is strontiurm 12. A composition according to claim 7 in which the metal of the naphthenate is lead.

13. A metal object which has been rendered resistant to corrosive attack through the formation thereon of a coating produced by treatment of the object with a composition comprising an inert carrier and as compounds providing a corrosion-inhibiting efiect a member of the class consisting of carboxylic acids and bivalent metal salts thereof and a member of the class consisting of aromatic carboxylic acids and bivalent metal salts thereof at least one of said members being present as a bivalent metal salt, the aromatic member being present in an amount at least equal to the amount capable of saturating the carrier alone.

14. A steel razor blade which has been rendered resistant to corrosive attack through the formation thereon of a coating produced on the blade by treatment thereof with a composition comprising a mineral oil, and as compounds providing a corrosion-inhibiting effect (1) a member of the class consisting of benzoic acid and bivalent metal salts thereof and (2) a member of the class consisting of a naphthenic acid and bivalent metal salts thereof, at least one of said members being present as a bivalent metal salt, member (1) being present in an amount at least equal to the amount capable of saturating the mineral oil alone.

15. A lubricating oil comprising, as compounds providing a corrosion-inhibiting effect, a member of the class consisting of carboxylic acids and bivalent metal salts thereof and a member of the class consisting of aromatic carboxylic acids and bivalent metal salts thereof, at least one of said members being present as a bivalent metal salt, the aromatic member being present in an amount at least equal to the amount capable of saturating the lubricating oil alone.

(R f e o lo e References Cited in the file of this patent 2,402,825 UNITED STATES PATENTS Detwiler 19, 2 2,366,074 Wasson Dec. 26, 1944 5 2,398,485 Wilson Apr. 16, 1946 10 Lovell et a1. June 25, 1946 Zisman Jan. 27, 1948 Bartelson et a1. July 17, 1951 Catcas et al Feb. 2, 1954 

1. A COMPOSITION FOR APPLICATION TO A METAL SURFACE TO RETARD THE CORROSION THEREOF WHICH COMPRISES AN INERT CARRIER AND AS COMPOUNDS PROVIDING A CORROSION-INHIBITING EFFECT A MEMBER OF THE CLASS CONSISTING OF CARBOXYLIC ACIDS AND BIVALENT METAL SALTS THEREOF AND A MEMBER OF THE CLASS CONSISTING OF AROMATIC CARBOXYLIC ACIDS AND BIVALENT METAL SALTS THEREOF, AT LEAST ONE OF SAID MEMBERS BEING PRESENT AS A BIVALENT METAL SALT, THE AROMATIC MEMBER BEING PRESENT IN AN AMOUNT AT LEAST EQUAL TO THE AMOUNT CAPABLE OF SATURATING THE CARRIER ALONE. 